Heat oven to 300 degrees F. Put on a kettle of water to boil. In a medium saucepan, bring cream and sugar to a simmer, stirring occasionally. Remove from heat; add chocolate and espresso powder. Let stand 1 minute; stir until chocolate melts and coffee dissolves. Whisk in yolks and vanilla until mixture is blended and smooth.

Pour chocolate mixture into 2 (6-ounce) heart-shaped or round ramekins or custard cups. Place ramekins in an 8-inch-square baking pan. Pour hot water into pan so that it comes halfway up sides of ramekins.

Bake 25 minutes or until almost set in centers. Remove ramekins to a wire rack; cool slightly. Serve warm and soft, or refrigerate up to 1 day. Garnish with dollops of whipped cream and chocolate shavings, if desired.